This invention relates generally to a pest repellent system and, more particularly, pertains to a system and method for efficiently sonifying and ridding an area of unwanted pests.
Noxious pests such as rats or mice have long caused havoc in many places because of the harm such pests cause to property. More importantly, these pests are disease carriers and a hazardous situation is created if such pests are permitted to occupy the same area as humans.
Many techniques have been employed to rid such areas of unwanted pests. The most common is to set out rat poison. However, this technique has obvious drawbacks.
Another technique presently gaining widespread popularity is one in which an area is sonified by blanketing it with ultrasonic signals that are above the human range of hearing and to which the pests are sensitive. Normally, this is in the range of 18 KHz to 30 KHz. It has been determined that some pests are sensitive only to frequencies at the low end of the range while other pests are sensitive to frequencies at the high end. However, the stated range of frequencies is required so that most unwanted pests, such as rats, pigeons, insects, etc., will be affected.
It has been found that the most efficient type of transducer for such a system is a piezoelectric device. However, these devices have extremely limited bandwidth and a single transducer is ineffective to produce signals over the entire bandwidth under consideration.
As noted more fully in my U.S. Pat. No. 3,872,472, if pests are exposed to ultrasonic energy of predetermined frequency for prolonged periods, they eventually become immune to the sound and they reappear. Even variable frequency signals that are regular with time become ineffectual after a period of time. That is, the rodents are able to accommodate themselves to such regular frequency variations.
In practice, it has been found that a minimal intensity level of sound is required to effectively eliminate rodents from an infested area. In other words, for maximum efficiency and effectiveness, the intensity of the sound at any point within the area to be treated should not fall below a minimum level.
It is thus the main object of the present invention to provide an improved ultrasonic pest repellent method and system which overcomes the disadvantages of the prior art methods and systems by providing ultrasonic point sources which produce pulse signals having a randomly varying frequency in the range of about 18 to 30 kilohertz and spacing the point sources in a given area to maintain the minimum sound intensity level at any point in the sonified portion at not less than 90 dB.